1. Field of the Invention
The invention relates to a computer storage device, and more particularly, to a method for reducing a variation range of a skew angle of a magnetic writing pole and a magnetic writing pole using the same.
2. Description of the Related Art
The hard-disk storage technology has been the main computer storage technology all the years. Currently, structure and operation mechanism of the hard disk drive still use a so-called ‘Winchester mode’, in which a magnetic head moves in a radial direction upon its corresponding disk surface whilst the disk rotates at high speed in a sealing cavity. As shown in FIG. 1, a conventional hard disk drive 10 includes one disk or multiple disks, a disk-driving motor, a read-write head assembly, a magnetic head driving device, and a read-write control circuit plus data read/write electronics and motor controlling electronics. The disk 11 is a magnetic storage medium operating to record information and rotates at high speed under driving of a spindle motor 12. The read-write head assembly includes a read-write head, a slider 13, and a suspension arm 14. The read-write head is packaged on the slider 13. In operation, a magnetic head driving device (voice coil motor) 16 drives the suspension arm 14 and the slider 13 to rotate around a pivot shaft 15 so that the slider 13 can be positioned above a predetermined magnetic track. Meanwhile, the disk 11 rotates at high speed, and the read-write head is positioned at a predetermined sector thereof, and thus facilitating data reading and writing thereon as flying over the disk surface thereof. FIG. 2 is a top view of a magnetic writing head. The magnetic writing head comprises a magnetic writing pole 23 and a return pole 22, both packaged on the slider 21. The magnetic writing pole 23 operates to write bit information.
With increase in a recording density of hard disk drives, the areal size of each recording bit gradually decreases. The magneto-crystalline anisotropy of the recording medium must be large enough or further increased to ensure the thermal stability of a recorded bit and, as a result, the magnetic writing field of the magnetic writing head needs to be increased. In a conventional perpendicular magnetic recording system, the width of a recorded magnetic track thereof is approximately the same as that of a magnetic writing pole. Therefore, as the recording density increases, the width of the magnetic track decreases and, therefore, the width of the magnetic writing pole needs to be reduced accordingly. However, reduction in the width of the magnetic writing pole often results in decrease of the magnetic writing field. Shingled magnetic recording scheme has been proposed to provide strong writing field as track density increases. In a shingled magnetic recording system, the width of the magnetic writing pole is no longer limited by the width of the magnetic track and a wider magnetic writing pole covering multiple magnetic tracks is used for recording and, therefore, a large enough writing magnetic field can be obtained. As shown in FIG. 3, the shingled magnetic recording system employs a method of partly overwriting a previous recorded magnetic track to record. The magnetic writing pole 30 in FIG. 3 sequentially writes magnetic tracks 31, 32, 33 and 34 from the top to the bottom, each magnetic track is partially overlapped with a previous recorded magnetic track (for example the magnetic track 33 overwrites part of the magnetic track 32, and the magnetic track 34 overwrites part of the magnetic track 33). The wider the writing pole, the stronger the writing field and the higher the recording density will be. It should be noted that a writing corner 301 of the magnetic writing pole 30 is the place having most significant effect on the recording performance of the shingled magnetic recording system.
In a shingled magnetic recording system as shown in FIG. 4, a magnetic writing pole 40 writes a current recording bit 422. The magnetic writing pole 40 needs to ensure that a previous recorded bit 421 and a previous recorded magnetic track 41 are not erased or partially erased. Bits following the current recording bit 422 that has been overwritten is to be rewritten during sequential movement of the magnetic writing pole 40. In addition, an angle between the normal direction of a trailing side of the magnetic writing pole 40 and the magnetic track 42 is referred to as a ‘skew angle’. As the magnetic writing head moves in a radial direction with the suspension arm as shown in FIG. 1, the skew angle θ increases or decreases accordingly. As skew angle θ varies, the erasing effect of the magnetic writing pole on a previous recorded bit (for example, bit 421) or a previous recorded magnetic track (for example, magnetic track 41) increases. For example, as the skew angle θ increases, the magnetic field generated around an edge ‘a’ of the magnetic writing pole 40 will increase possibility of erasing the previous recorded bit 421, and as the skew angle θ decreases, the magnetic field generated around an edge ‘b’ of the magnetic writing pole 40 will increase possibility of erasing the previous recorded magnetic track 41. FIG. 5 illustrates relationship between a write-in error rate of the shingled magnetic recording system and a variation range of the skew angle. It can be seen that as the variation range of the skew angle increases, the write-in error rate increases significantly Therefore, it is of great importance for the shingled magnetic recording system to reduce the variation range of the skew angle θ so as to reduce the interference of the magnetic writing pole 40 to the previous recorded bit 421 and the previous recorded magnetic track 41.
So far, the magnetic writing pole of a shingled magnetic recording system uses only one writing corner for shingled magnetic recording. Therefore, as the magnetic writing pole moves from the innermost track to the outermost track in a radial direction, the writing corner moves along therewith and crosses all magnetic tracks. A variation range of a skew angle θ thereof is comparatively large (normally 18°-30°, and thus a high write-in error rate of the shingled magnetic recording system happens at those tracks corresponding to high skew angle.